Russell McMahon email (remove spam text)
What I need to do is detect a human presence in a range of up to 10
meters max. The person would be in line of sight.
It would be ideal if the 'target device' is passive (ie. requires no
Possibly something as simple as fluorescent (or similar) strip(s) sewn
into a garment that can be 'seen' by a detector. The only problem is the
different lighting situations
Consider doppler radar.
These were all the rage for door openers before PIRs took over.
Range depends on power and aerial.
While you can use the commercial Gunn effect oscillator commercial designs
eg Philips you can roll your own using eg a SAW oscillator.
A Wireless World article many years ago (70's? 80's?) used a push pull
oscillator on PCB.
Here's a trad secret you won't hear about anywhere in the literature that
I'm aware of
Filter the return signal with a bandpass filter to detect the "joint
articulation frequency" from human joints. I forget the frequency but AFAIR
its around 17 to 25 Hz range. Playing will indicate a very human specific
response frequency. This helps eliminate false triggering from curtains,
doors, animals falling objects etc.
Aerial beam pattern will assist detection of only what you want to see.
Getting a wide or multidirectional aperture may be "interesting".
What can one man* do?
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